From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison table of different radiator tube types, detailing performance under various bonnet ventilation conditions.
| Identifier | Morton\M19\ img161 | |
| Date | 27th March 1930 guessed | |
| TYPE OF RADIATOR TUBE CRITICAL AIR TEMPº. The difference between the top water temp. and Ats (St.{Capt. P. R. Strong}) subtracted from 100º. This temp. represents that at which the car will eventually boil in still air if driven sufficiently long full throttle. 60 MPH. No bonnet ventilation. | All out bonnet vent. | All out Vertical bonnet louvres Small Hexagonal ended American tube .305" across flats .255" dia. round. No. of Dents. 18. | 46. | 38. | 46. Large Hexagonal Ended American Tube. Hexagon .360" across flats Centre .209" Dia. round No. of Dents. 20. | 41.5 | 38. This reading requires confirmation. | 42.5 Present standard tube. 6/7# mm. Round Z.79448. 4 Dents/tube | 39.5 | 31. | 38.5 Square tube Z.81389. 6 mm. square centre tube expanded to 7# mm. horizontally only. i.e. 1# mm. vertical waterways. No horizontal waterways. | 38. | 29.5 | 39.0 Tests on 1-EX. Brooklands. Car weight 48 cwt. Axle 11x41. All radiator dimensions 25.3 X 23.7. | ||